Purple loosestrife (Lythrum salicaria) is an alien invasive species that is considered a threat to wetland plant community biodiversity. In PEI National Park, annual monitoring focuses on distribution within the park and individual wetlands, as well as density once detected. Assessing management effectiveness is also a goal of the monitoring program. Each year all known sites containing purple loosestrife are surveyed during the blooming period and management actions (i.e. plant or seed removal) implemented. Annual purple loosestrife density is calculated separately for each impacted wetland area and reported as the number of plants per m2. All purple loosestrife plants found within PEI National Park are removed (dug or cut depending on conditions) annually. An index of purple loosestrife density within wetlands is calculated and compared against ecological integrity thresholds derived from existing literature and expert opinion.